1. Field of the Invention
The present invention pertains to techniques for sealing cylindrical members to circumscribing conduits. More particularly, the present invention relates to well tools, such as well packers, for selectively sealing a tubing string, for example, to a surrounding well conduit such as provided by casing or well liner.
2. Description of Prior Art
Well packers and other well tools are known for selectively sealing and/or anchoring a tubing string, for example, to a surrounding well conduit or liner. Such well tools may be set in the sealing/anchoring configuration by manipulation of a tubing string from which the tools are suspended, or by application of hydraulic pressure by means of the tubing string, for example. The tool may be released from its set configuration and retrieved from the well by appropriate manipulation of the tubing string.
Anchoring devices are known to include a plurality of slip members with opposed camming surfaces which cooperate with complementary opposed frustoconical wedging surfaces, for example, whereby the slip members are extendable radially into gripping engagement with the well conduit in response to relative axial movement of the wedging surfaces. Sealing devices are known which include annular resilient seal members which expand radially into sealing engagement with the well conduit in conjunction with axial compression of the sealing members. Thus, such packers may be set, rendering the sealing mechanism and the anchoring mechanism both in appropriate engagement with the surrounding well conduit, in response to relative longitudinal movements of various packer components, effected either hydraulically or mechanically.
A well packer may be locked in its set configuration, and permit variation of the well pressures and/or manipulation of the tubing string without unsetting the packer. Packers of various designs may be retrieved from the well by appropriate manipulation of the tubing string, for example. In some instances, the packer may be released from its set configuration by a straight pull upwardly on the tubing string. Pressure-responsive clamping or holding devices are known for preventing unwanted longitudinal movement of the tubing string which might otherwise release the packer prematurely. Such longitudinal tubing string movement may be urged, for example, in response to a variation in tubing string length due to temperature variations, or an increase in down-hole fluid pressure acting upwardly on the tubing string.
While packer anchoring devices utilizing opposed wedging systems may resist disengagement urged by pressure differentials acting on the packers either upwardly or downwardly, where the packer sealing mechanism and anchoring mechanism are fixed in set configuration by a common locking device, any slippage in the packer components in response to forces acting to unset the anchoring mechanism might dislodge, or interrupt the sealing engagement between the packer and the surrounding well conduit. Once the integrity of the sealing engagement of the packer is thus destroyed, it may difficult or impossible to regain the sealed connection between the tubing string and the conduit. It is therefore desirable to provide a well tool which may be set and locked in sealing engagement with a surrounding well conduit independently of the setting and locking of the anchoring engagement of the well tool to the conduit.